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The Sexual-Response Cycle: What Happens to Our Bodies During Sex

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WebMD Feature

While most of us are sure that we like to have sex, most of us also haven't spent much time thinking about what happens physiologically while we are engaged in the act. Masters and Johnson (two groundbreaking sex therapists) coined the term "sexual-response cycle" to mean the sequence of events that happens to the body when a person becomes sexually aroused and participates in sexually stimulating activities (intercourse, masturbation, foreplay, etc.).

The sexual-response cycle is divided into four phases: excitement, plateau, orgasm and resolution. There is no distinct beginning or end to each phase -- they're actually all part of a continuous process of sexual response.

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Keep in mind that this is a very general outline of what happens to each of us as we become sexually aroused. There is much variation among individuals, as well as between different sexual events.

Simultaneous Orgasms

Both men and women go through all four phases, except the timing is different. Men typically reach orgasm first during intercourse, while women may take up to 15 minutes to get to the same place. This makes the likelihood of simultaneous orgasm during intercourse a rare event.

Phase One: Excitement

This phase usually begins within 10 to 30 seconds after erotic stimulation, and can last anywhere from a few minutes to many hours.

Men: The penis becomes slightly erect. A man's nipples may also become erect.

Women: Vaginal lubrication begins. The vagina expands and lengthens. The outer lips, inner lips, clitoris and sometimes breasts begin to swell.

Both: Heart rate, blood pressure and breathing are all accelerated.

Phase Two: Plateau

The changes that started in the excitement phase continue to progress.

Men: The testes are drawn up into the scrotum. The penis becomes fully erect.

Women: The vaginal lips become puffier. The tissues of the walls of the outer third of the vagina swell with blood, and the opening to the vagina narrows. The clitoris disappears into its hood. The inner labia (lips) change color (although it's a bit hard to notice). For women who've never had children, the lips turn from pink to bright red. In women who've had children, the color turns from bright red to deep purple.

Both: Breathing and pulse rates quicken. A "sex flush" may appear on the stomach, chest, shoulders, neck or face. Muscles tense in the thighs, hips, hands and buttocks, and spasms may begin.

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